The role of the Bioanalytical (Mass Spectrometry) Core (BMSC) is to provide cost effective, state-of-the-art instrumentation to Members of the Digestive Disease Research Center for structural analysis of biological molecules and for qualitative and quantitative assays of nutrients and metabolites in physiologic fluids. The Core is directed by Dr. Richard Caprioli and co-managed by Dr. David L. Hachey. The Core has three triple quadrupole LC/MS instruments, four GC/MS systems and a matrix-assisted laser desorption ionization (MALDI) mass spectrometer. Laboratory personnel assist users in developing HPLC and MS methods, assist in experimental design, develop standard operating procedures, maintain QC records on instrument performance and maintenance history, perform routine assays for Members and train students and fellows in the theoretical and practical aspects of mass spectrometry. The Core is run as an open-access facility in which users are expected to prepare their own samples and to operate the instruments. Administrative staff monitors the use of the instrument facilities by Members and prepares reports on utilization for the Center director. The Core has three dedicated operators for each major class of instrument who are available to assist users as necessary. Twenty-four Members have requested mass spectrometry services from the Core. The most frequently requested services are those related to identification and characterization of proteins by mass spectrometry (services C, D and E), followed by requests for development of new methods (service G) and assistance with data analysis and interpretation (service H). Other services offered are quantitative analysis of prostaglandins and oxidized lipids (services A, B), quantitation of micronutrients in physiologic fluids (service F), and education and training (service I).